We don't seem to use the return value of riak_kv_get_fsm:start_link/4 anywhere, but it might be a good idea for sanity to have it return consistently. If sidejob is not enabled (first case), it returns {ok, Pid}, etc from gen_fsm:start_link, but if it is, we return ok, or the {ReqId, {error, overload}} from overload_reply.